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Episode 3 - Roots Against Erosion

February 2021

The Bitterroot River is dynamic and its channel moves back and forth across its floodplain.  Though channel migration is a natural process, human influence can impact the rate of migration.  For example, the absence of native riparian vegetation can increase rates of erosion, speeding up channel migration.

Over the past 25 years, the Bitterroot River has been migrating eastward into the area of Skalkaho Bend Park. Because the park lacks riparian habitat, like woody shrubs, the river has been eating away at the open grass area, eroding the stream bank.  In a study of the park, renowned geomorphologist Karin Boyd predicted that the bank is likely to have eroded all the way to the C&C ditch on the east side of the property by 2040. If this were to happen, the park would effectively be broken into two segments, which would severely disrupt public access.

The Bitter Root Water Forum is working with the City of Hamilton on a project to address the potential erosional loss of park land at Skalkaho Bend.  “Roots Against Erosion” will use plants to slow erosion while simultaneously enhancing riparian habitat.

Geum Environmental Consulting, a local firm specializing in restoration project design and ecological planning, was hired to lend their expertise.  After considering the options, Geum, the Water Forum, and Hamilton’s Director of Public Works, Donny Ramer, determined the best strategy is to use the roots of native plants to slow the erosion at the park. Chris Clancy, retired fisheries biologist for FWP added, “This is about as ecologically sound a project as you can build along the river”.

The project involves excavating a shallow, 1500-foot-long depression, or “swale,” at the park, planting this excavated area with native woody riparian plants, and surrounding the plants with temporary wildlife fencing.  The fencing will have multiple crossings to allow wildlife and park visitors access through the planted area.  At least 97% of the proposed plantings are willows, known for their strong and resilient root webs.

Willows are an optimal species for this site since they have a strong root system but don’t typically grow more than 10 feet tall.  This will ensure that the park can be protected while the incredible viewshed is maintained.  For species and habitat diversity, dogwood, cottonwood, aspen, and serviceberry will also be planted. The project’s entire footprint covers a total of 1.5 acres, or roughly 2% of the total park land.

The planting area is set back from the bank to give the plants time to establish a strong root network before the river is predicted to reach them.  Because these plants need time to grow roots strong enough to withstand a flowing river, the project will take place this Spring.  Planting now will help prevent expensive and invasive alternatives in the future, such as armoring the bank with angular rock known as riprap – typically a last-resort measure to stop a river in its tracks.

Ed Snook, a retired Bitterroot National Forest hydrologist, said, “The City has a chance to be proactive here, which is rare when it comes to these kinds of projects.  This is a great way to accomplish the long-term goals of keeping the park and the C&C Ditch intact, with a low-impact, ecological approach that enhances native habitat.  The sooner this project is implemented, the more likely it is to succeed.”

The Montana Department of Environmental Quality and Bitterroot Audubon Society have provided funding for the project, so the City is not being asked to shoulder any construction costs.  Other than removing the temporary fencing in about 5 years, the project is designed to have a low maintenance burden.

The Water Forum’s Executive Director, Heather Barber, noted that the project will have excellent benefits for the community as well as natural resources. “Skalkaho Bend has become such a treasured spot for so many of us in the Valley.  The Water Forum is here to help the City do what’s best for the park, the river, and the community.  We’re really looking forward to getting folks involved in this effort to preserve the park for the future generations to enjoy.”

She added that signage at the park and future field trips will provide a tremendous opportunity for continued education about river movement and riparian areas.  The Water Forum is working with local educators to get youth and adults engaged in the planting process, as well as participating in nature walks and project monitoring.

If you’re interested in learning more about the project check out this webpage for Frequently Asked Questions and a Zoom presentation.

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